Telstra...
1) Tipping doesn't make any more or less sense than speaking English. But I'm not learning Esperanto or whatever just because someone else thinks English doesn't make sense. Nor am I going to start driving on the left side of the road.
Nor, importantly, am I going to go to Britain and drive on the right side of the road; nor am I going to go to India and demand a big slab of beef ribs.
Customs are customs, and unless someone is being hurt by them (and I don't consider having to cough up a fraction more cash being hurt; and while I do believe that waitstaff are being hurt, it's the labor laws hurting them rather than the custom of tipping), there's no reason to change them.
2) Cater waiters are tipped by the host, just as if in a restaurant (the one who pays the bill leaves the tip). The bartender is usually tipped by the guests, even if it's open bar, but by the host, too. The band leader or the dj should be tipped as well. And if you can afford $25k for just the catering, an extra five grand isn't going to hurt you that much... you have to take that sort of thing into account when you're budgeting.
3) Not all restaurants take advantage of the "direct wage" loophole in the labor laws... that mostly occurs in small diners and huge chains. Cheap restaurants, if you will. In a lot of the restaurants I patronize, the waitstaff make more than I do. And I still tip them.
4) Cheap-ass motherfuckers piss me off. I'm sure you're merely curious about the custom, Telstra (though I wonder, were you planning on hosting a large wedding reception?), but a lot of the people posting against the practice of tipping simply resent having to cough up one penny more than is printed on the menu. I say if such persons are so concerned about costs, they should stay home and cook for themselves.
I mean, look at all the various sales and service taxes we pay... hotel tax, airport use tax, smog tax... if you walk out of any place having paid only the printed price and nothing else, you've managed a minor miracle. So what's a few bucks more?